Auxiliary power units (APU's) have been used on board aircraft to provide power to support auxiliary equipment such as electrical systems, pressurized hydraulic systems, environmental control systems typically powered with the aircraft positioned on the ground. These APU's were problematic in that they were a source of significant weight and cost. It has been proposed to replace these APU's with auxiliary power and thrust units (APTU's), as seen in U.S. Pat. No. 6,247,668. The APTU's serve not only to provide power to auxiliary equipment but can also serve to provide additional thrust power to the aircraft at a time of takeoff and/or climb of the aircraft.
A need exists for APTU's which serve to provide the aircraft an efficient power source for operating hydraulic, electrical and environmental systems typically while the aircraft is on the ground during boarding and de-boarding operations and serve to provide the aircraft an additional thrust source at the time of takeoff and climbing to altitude. With the need for such a versatile power system source as the APTU, there is also a need to improve on its performance, reliability and versatility to operate within limited space provided on board the aircraft.